Numerous systems are known for, in particular, classifying articles by optical characteristics, such as their colour. In U.S. Pat. No. 2,678,725, a classification system is described in which two light beams of different colours are directed at articles to be classified. The system is arranged to provide dual outputs, one of which is related to the chromaticity of the articles, this being defined as their redness or blueness, and the second output being related to the brightness of the article, namely its lightness or darkness.
According to U.S. Pat. No. 3,675,769, a mixture of potatoes and stones and soil is conducted beneath a source of visible and invisible light. A detection system responsive to the light reflected by the mixture of materials classifies the material monitored into two categories based upon the ratio of their reflectivities within selected radiant energy bands. Associated sorting means directs useful product into an appropriate collection feature while discarding the unwanted stones and soil.
U.S. Pat. No. 3,776,381 provides a method for sorting products in which light reflected from product is monitored by light-sensitive cells to detect products that are too light, too dark or otherwise defective. U.S. Pat. No. 3,910,701 provides a method and apparatus for measuring light reflectance, absorption and/or transmission, in which light of different wavelengths is directed towards a test piece, and reflected and/or transmitted light from the test piece is monitored by a light-responsive sensor.
U.S. Pat. No. 3,939,983 relates to apparatus for grading and sorting tobacco, in which tobacco leaves are scanned by detectors monitoring the reflectivity of the leaves. Outputs from the detector control an ejection system for separating those leaves having the required reflectivity characteristics from those leaves which are to be discarded. U.S. Pat. No. 4,081,362 is directed to specific mechanical aspects of a fruit sorter, in which a colour sorting system is applied.
In U.S. Pat. No. 4,095,696, a tomato monitoring system making use of three photodetectors, each having a different spectral response, is described. Each detector monitors a different wavelength of light reflected from the tomato. Logic circuitry operating on the outputs of the three detectors enable red tomatoes to be separated from all other articles on the conveyor, including dirt and rocks. U.S. Pat. No. 4,120,402 describes a further product sorter suitable for separating green tomatoes from red tomatoes and also for the removal of foreign objects such as dirt and debris from a flow of tomatoes to be sorted. This system uses two pairs of phototransducers, each having a respective specific colour filter.
U.S. Pat. No. 4,134,498 discloses a further sorting system in which light reflected from articles of two predetermined wavelengths is monitored and processed to provide a classification signal functionally related to the ratio of the respective signals at the different wavelengths. A further system using two different wavelengths of light is described in U.S. Pat. No. 4,146,135, in this case directed to the detection of peach pits and peach pit fragments remaining in peach halves following a pitting operation.
Yet another system employing radiant energy at bands of two mutually different wavelengths is disclosed in U.S. Pat. No. 4,186,836. Downstream signal processing in conjunction with removal devices enables the required sorting action to be achieved.
U.S. Pat. No. 4,204,950 describes a produce grading system in which reflected light from an object is monitored in four colour bands, two in the visible range and two in the invisible range. Comparison of colour combinations enables the system to detect the presence of a desired colour or an undesired colour, and also to determine the characteristics of the product, namely whether it is vegetable or non-vegetable matter. In U.S. Pat. No. 4,281,933, fruit sorting apparatus is described in which the colour of the fruit is detected by directing light signals onto opposite sides of the fruit and processing electronic signals derived from the reflected light levels to produce the required information to enable suitable sorting action to be effected.
German Published Patent Specification No. 2,319,721 describes a further optical sorting system while yet another such arrangement is disclosed in Japanese Patent Specification No. 54-144662.
One or more of a variety of problems or deficiencies may be identified in many known systems, such as those adverted to above, although not all of the problems subsequently indicated are necessarily experienced in every such system. Nonetheless, many optical sorting systems are distinguished by substantially total dependence on directly reflected light from the product surface to provide information for the sorting process. Many such systems are also limited to typically one or two spectral bands of illumination, and even where more than two such bands are employed, the dependence on reflected light remains. A very particular deficiency of many existing systems is an inability to detect or analyse small features. Furthermore, the majority of existing or known systems are unable to identify defects. Even in systems capable of identifying the presence of defects, classification of any particular defect as to its nature is not generally available. The detection of different surface textures and the identification of surface imperfections of a variety of different kinds are also features not in general available in known systems. A further specific limitation is the inability of the majority of existing optical sorting systems to operate on anything other than a limited area of the product. Thus defects outside the field of monitoring or observation of the system may go undetected. A related deficiency or problem is a reduced level of inspection sensitivity away from the central region of the product lying directly under the monitoring light source.
It is an object of the invention to provide an information gathering system overcoming at least one of the foregoing deficiencies or problems. It is a specific object of the invention to provide a product sorting system in which one or more of the foregoing problems or deficiencies are addressed.